Semiconductor device having a fuse element

ABSTRACT

A portion-to-be-melted of a fuse is surrounded by plates, so that heat to be generated in a meltdown portion of the fuse under current supply can be confined or accumulated in the vicinity of the meltdown portion of the fuse. This makes it possible to facilitate meltdown of the fuse. The meltdown portion of the fuse in a folded form, rather than in a single here a fuse composed of a straight-line form, is more successful in readily concentrating the heat generated in the fuse under current supply into the meltdown portion, and in further facilitating the meltdown of the fuse.

This application is based on Japanese patent application No.2003-288829, the content of which is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and inparticular to a semiconductor device mounted with a fuse.

2. Description of the Related Art

Mounting of a fuse on a semiconductor device makes it possible to adjustvalue of resistors used in the semiconductor device or replace adefective element with a normal element, by once disconnecting the fuse.This technique of replacing a defective element with a normal element istypically applied to redundancy design of the semiconductor memorydevice. Disconnection of the fuse is often achieved by blowing it offwith a laser. The method of blowing the fuse off using the laser,however, raises several problems.

A first problem resides in that a position of disconnection of the fusemust be apart from other elements by a predetermined distance so as toavoid any possible influences of the laser-assisted disconnection of thefuse, and this increases the device size in view of securing asufficient space therefor.

The next problem is that one or two dedicated lithographic process stepsare further required to form the fuse in addition to the general processsteps, and this consequently results in larger cost and longer processtime. More specifically, the fuse will generally have an interlayer filmformed thereon, so that it is necessary, in the final process step, toform an opening for the convenience of laser irradiation in theinterlayer film so as to adjust the thickness of the interlayer film onthe fuse. In evaluation of any products incorporated with the fuse, itis essential to carry out a series of process steps of “characteristicinspection”, “disconnection of fuse by laser irradiation” and“characteristic re-inspection”. This undesirably results in furtherelongation of the process steps and increase in the cost.

To solve the above-described problems in the laser-assisteddisconnection of the fuse, a proposal is made on current-assistedmeltdown of the fuse in place of using the laser. As one typical methodof facilitating the current-assisted disconnection of the fuse; JapaneseLaid-Open Patent Publication No. 2000-40790 discloses a procedure ofnarrowing as possible a meltdown portion of the fuse by oblique ionimplantation through a mask formed on the meltdown portion of the fuse.

The fuse disclosed in Japanese Laid-Open Patent Publication No.2000-40790 can certainly reduce current and/or voltage necessary formeltdown the fuse, but further reduction in the current and/or voltagefor meltdown will be necessary if the semiconductor devices mounted withthe fuse are desired to be applied to circuits driven under low voltage,in consideration of influences on other elements.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asemiconductor device mounted with a fuse adapted to a smaller currentand/or voltage for the meltdown, characterized in having a fuse possiblymelted by further smaller current and/or voltage.

According to the present invention, there is provided a semiconductordevice disposed on a substrate, and has a conductor possibly bedisconnected upon being supplied with current, wherein the semiconductordevice has at least one parallel plate composed of a flat surface inparallel to the direction of current flow in the vicinity of theconductor.

The semiconductor device of the present invention may further compriseat least one vertical plate composed of a flat surface normal to thedirection of current flow in the vicinity of the conductor, and thevertical plate may have an opening which allows a current entranceportion or a current exit portion to pass therethrough.

In the semiconductor device of the present invention, at least oneparallel plate may comprise a pair of flat surfaces opposed to eachother in parallel to the direction of current flow to thereby configurefirst and second parallel plates placing the conductor in between; ormay comprise a pair of flat surfaces opposed to each other in parallelto the direction of current flow to thereby configure first and secondparallel plates placing the conductor in between, and a pair of flatsurfaces opposed to each other and normal to the first and secondparallel plates to thereby configure third and fourth parallel platesplacing the conductor in between.

In the above-described semiconductor device of the present invention, atleast one parallel plate may be disposed between a semiconductor elementor wiring, which is arranged on a flat surface in parallel to saiddirection of current flow, and the conductor.

In the above-described semiconductor device of the present invention,the conductor may have a straight-line form, or may have a form such asextending unidirectionally and being folded at least once. In particularin the latter case, the conductor may have a forward straight portionextending in a single direction, and a backward straight portionextending back in a direction opposite to the single direction, and theconductor may further comprise a normal straight portion normal to thesingle direction, which connects the forward straight portion and thebackward straight portion.

In the above-described semiconductor device of the present invention,the substrate may be configured as having a transistor formed thereon,wherein the conductor is supplied with the current by turning thetransistor on, and the transistor may be a MOSFET.

In the above-described semiconductor device of the present invention,the conductor may be any of a material mainly composed of copper (Cu),doped polysilicon, silicon-germanium alloy and silicide.

As has been explained in the above, in the semiconductor device mountedwith the fuse of the present invention, a portion-to-be-melted of thefuse is surrounded by the plates, so that heat to be generated in themeltdown portion of the fuse under current supply can be confined oraccumulated in the vicinity of the meltdown portion of the fuse. Thismakes it possible to facilitate meltdown of the fuse. The meltdownportion of the fuse in a folded form, rather than in a singlestraight-line form, also makes it possible to more readily concentratethe heat generated in the fuse under current supply into the meltdownportion, and to further facilitate the meltdown of the fuse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing a form of a fuse according to a firstembodiment of the present invention;

FIG. 1B is a sectional view taken along line I-I in FIG. 1A;

FIG. 2 is a plan view showing a form of a fuse according to a modifiedexample of the first embodiment;

FIG. 3 is a sectional view taken along line I-I in FIG. 2;

FIG. 4A is a plan view showing a form of a fuse according to a secondembodiment of the present invention;

FIG. 4B is a sectional view taken along line II-II in FIG. 4A; and

FIG. 5 is a sectional view taken along line in FIG. 4A.

DETAILED DESCRIPTION OF THE INVENTION

The following paragraphs will specifically describe the semiconductordevice mounted with the fuse composed of the conductor according to thepresent invention referring to preferred embodiments, wherein they areto be understood as being merely for the purpose of description and notof limitation.

Embodiment 1

A first embodiment of the present invention will be explained referringto FIG. 1A and FIG. 1B. The first embodiment shows a case where a fuse,which is a straight-line-formed conductor, is disposed in parallel tothe surface of a semiconductor substrate. FIG. 1A is a plan view of thefuse, and FIG. 1B is a sectional view taken along line I-I in FIG. 1A.

As shown in FIGS. 1A and 1B, a fuse 100 is provided in a secondinterlayer dielectric film 104 on a first interlayer dielectric film 102on a semiconductor substrate 101. It is to be noted that the secondinterlayer dielectric film 104 is practically composed of a plurality ofinterlayer dielectric films although it is illustrated herein as asingle layer for the simplicity of explanation. The fuse 100 is coveredwith a lower plate 103 and an upper plate 114, which compose a pair ofparallel plates, respectively on the lower and upper portions of a fusemeltdown portion 107, and with via plugs 106, 113 filled in viaholes105, 112 on the side portions of the fuse meltdown portion 107. Theupper and lower via plugs 113, 106 are interconnected through padelectrodes 108 formed at the same time with the fuse 100, and the viaplugs 106, 113 thus configure, together with the pad electrodes 108,side plates 126 and 127 both of which correspond to a pair of verticalplates, on each of lateral sides, respectively, of the fuse 100.

The fuse 100 is melted down by supplying a predetermined energy ofcurrent from a current entrance terminal 110 towards a current exitterminal 111 (the directionality may be inverted), which are formed atthe same time with the fuse meltdown portion 107. With the aid of ON/OFFoperation of an unillustrated transistor, which is typically a MOSFET,connected to the current entrance terminal 110, the ON operation cansupply the current for meltdown, and OFF operation can stop supply ofthe current for meltdown.

When a predetermined energy of current is supplied from the currententrance terminal 110 towards the current exit terminal 111, heat isgenerated at the fuse meltdown portion 107 of the fuse 100 and isconcentrated thereto after being intercepted and reflected by the plates114, 103, 126, 127 on the vertical and lateral sides, so as to causeeasy meltdown. At the same time, the conductor to be scattered aroundcan be blocked by the lower plate 103, upper plate 114 and side plates126, 127, and is prevented from reaching the other elements arrangedoutside these plates.

Although this embodiment adopted a structure in which the meltdownportion of the fuse is almost completely enveloped by disposing theconductor plates on the vertical and lateral sides of the fuse, thepresent invention is by no means limited thereto. More specifically, inan exemplary case where any other element resides on either of the upperand lower sides of the meltdown portion of the fuse, it is alsoallowable to adopt a structure in which only the upper and lower sidesare covered with the upper plate 114 and lower plate 103, while leavingthe lateral sides uncovered. In the case that any other element disposedon only either side of the upper and lower sides, as far as preventionof the scattered conductor during the fuse meltdown is considered, it isall enough to dispose the plate only between the element in concern andthe fuse. Even in such a case, it is, however, still preferable todispose the plates both on the upper and lower sides, in view ofconfining the heat generated during the fuse meltdown in the vicinity ofthe fuse meltdown portion 107.

Next, a modified embodiment of the first embodiment will be explainedreferring to FIGS. 2 and 3. FIG. 2 is a plan view of the fuse, and FIG.3 is a sectional view taken along line I-I in FIG. 2. The modifiedembodiment adopts a configuration in which the meltdown portion of thefuse is configured as extending unidirectionally and being folded atleast once, a plurality of times for example, rather than as beingformed in a straight-line form, and more specifically, configured ashaving a forward straight portion extending in a single direction, abackward straight portion extending back in a direction opposite to thesingle direction, and a normal straight portion normal to the singledirection, which connects the forward straight portion and the backwardstraight portion.

As shown in FIGS. 2 and 3, a fuse 200 is provided in a second interlayerdielectric film 204 on a first interlayer dielectric film 202 on asemiconductor substrate 201. It is to be noted that the secondinterlayer dielectric film 204 is practically composed of a plurality ofinterlayer dielectric films although it is illustrated herein as asingle layer for the simplicity of explanation. The fuse 200 is coveredwith a lower plate 203 and an upper plate 214 on the lower and uppersides thereof, and with via plugs 206, 213 filled in viaholes 205, 212on the side portions, respectively, thereof. The upper and lower viaplugs 213, 206 are interconnected through pad electrodes 208 formed atthe same time with the fuse 200, and the via plugs 206, 213 thusconfigure, together with the pad electrodes 208, side plates 226 and 227on both lateral sides, respectively, of the fuse 200.

The fuse 200 is melted down by supplying a predetermined energy ofcurrent from a current entrance terminal 210 towards a current exitterminal 211. The fuse 200 has, on the current entrance terminal 210side thereof, a first forward straight portion 251; a first backwardstraight portion 253; a first normal connection portion 252 whichconnects the first forward straight portion 251 and the first backwardstraight portion 253; a second forward straight portion 255 extendingback in a direction opposite to the direction of the first backwardstraight portion 253; a second normal connection portion 254 whichconnects the first backward straight portion 253 and the second forwardstraight portion 255; a second backward straight portion 257 extendingback in a direction opposite to the direction of the second forwardstraight portion 255; a third normal connection portion 256 whichconnects the second forward straight portion 255 and the second backwardstraight portion 257; a third forward straight portion 259 extendingback in a direction opposite to the direction of the second backwardstraight portion 257; a forth normal connection portion 258 whichconnects the second backward straight portion 257 and the third forwardstraight portion 259; a third backward straight portion 261 extendingback in a direction opposite to the direction of the third forwardstraight portion 259; a fifth normal connection portion 260 whichconnects the third forward straight portion 259 and the third backwardstraight portion 261; a forth forward straight portion 263 extendingback in a direction opposite to the direction of the third backwardstraight portion 261; a sixth normal connection portion 262 whichconnects the third backward straight portion 261 and the forth forwardstraight portion 263; a forth backward straight portion 265 extendingback in a direction opposite to the direction of the forth forwardstraight portion 263; a seventh normal connection portion 264 whichconnects the forth forward straight portion 263 and the forth backwardstraight portion 265; a fifth forward straight portion 267 extendingback in a direction opposite to the direction of the forth backwardstraight portion 265; a eighth normal connection portion 266 whichconnects the forth backward straight portion 265 and the fifth forwardstraight portion 267, and further the current exit terminal 211 whichcontacts the fifth forward straight portion 267.

Theoretically, a third forward straight portion 259, which resides inthe midst of nine straight portions, that is first to fifth forwardstraight portions and first to forth backward straight portions, issupposed to be most likely to melt.

Since thus-configured fuse 200 is enveloped by the lower plate 203,upper plate 214 and side plates 226, 227, which are the conductorsvertically and laterally cover the fuse, heat generated at the fuseunder current supply thereto is reflected and confined within a spacesurrounded by these plates, so that the fuse can readily be melted down.In thus-configured fuse 200, when a predetermined energy of current issupplied from the current entrance terminal 210 towards the current exitterminal 211, summation of heat generated in hatched portions 281 (whichis heat generating region outside the fuse 200) outside the fuse 200 andheat generated in hatched portions 282 (which is heat generating regioninside the fuse 200) inside the fuse 200 is further caused, and thissuccessfully promotes the meltdown of the third forward straight portion259 which resides in the center portion as being sandwiched by thehatched portions 281. Therefore the fuse 200 can more readily be melteddown.

A conductive material available herein for composing the fuses 100, 200may be any of a material mainly composed of copper (Cu), dopedpolysilicon, silicon-germanium alloy and silicide.

Embodiment Example 2

The foregoing embodiment described a case where the fuse was disposed inparallel to the surface of the semiconductor substrate. Then, a secondembodiment will describe a case where the fuse is disposed normal to thesurface of the semiconductor substrate referring to FIG. 4A, FIG. 4B andFIG. 5. FIG. 4A is a plan view of the fuse, FIG. 4B is a sectional viewtaken along line II-II in FIG. 4A, and FIG. 5 is a sectional view takenalong line in FIG. 4A.

As shown in FIGS. 4A and 4B, a fuse 400 is disposed in a secondinterlayer dielectric film 404 on a first interlayer dielectric film 402on a semiconductor substrate 401. It is to be noted that the secondinterlayer dielectric film 404 is practically composed of a plurality ofinterlayer dielectric films although it is illustrated herein as asingle layer for the simplicity of explanation. The fuse 400 is coveredwith a lower plate 403 and an upper plate 414 on the lower and uppersides, respectively, thereof, and with via plugs 406, 413, 433 filled inviaholes 405, 412, 432, respectively, on the side portions thereof. Themiddle and lower via plugs 413, 406 are interconnected through padelectrodes 408. The middle and upper via plugs 413, 433 areinterconnected through pad electrodes 428. The fuse 400 has a currententrance terminal 410 and a current exit terminal 411, and currentsupplied to the current entrance terminal 410 flows through a via-plugmeltdown portion 423 filled in a viahole 422 to reach the pad electrode407, and further flows through a via-plug meltdown portion 453 filled ina viahole 452 to reach the current exit terminal 411. Current supply tothe current entrance terminal 410 supposed to result in meltdown ofeither of the via-plug meltdown portions 423, 453, but it is alsoallowable that the pad electrode 407 interconnecting the via-plugmeltdown portions 423, 453 is melted off. The pad electrode 407 istherefore formed so as to have a width as narrow as possible as shown inFIG. 4A (of course narrower than the width of the current entranceterminal 410 and current exit terminal 411), but slightly wider than thewidth of the via-plug meltdown portions 423, 453. It is furthernecessary, as shown in FIG. 5, to arrange the via-plug meltdown portions423, 453 as close to each other as possible so as to allow heatconcentration. It is still further necessary, as shown in FIG. 4B, toconfigure the side plates 426, 427 both of which are composed of the viaplugs 406, 413, 433 and the pad electrodes 408, 428 on both sides of thefuse 400, in order to prevent the heat generated at the via-plugmeltdown portions 423, 453 from dissipating outwardly.

When a predetermined energy of current is supplied from the currententrance terminal 410 towards the current exit terminal 411, heat isgenerated at the via meltdown portions 423, 453 of the fuse 400, andoptionally at the pad electrode 407 which may be a meltdown portion, andis concentrated thereto after being intercepted and reflected by theplates 414, 403, 426, 427 on the vertical and lateral sides, so as tocause easy meltdown. At the same time, the conductor to be scatteredaround can be blocked by the lower plate 403, upper plate 414 and sideplates 426, 427, and is prevented from reaching the other elementsarranged outside these plates.

Although this embodiment adopted a structure in which the meltdownportion of the fuse is almost completely enveloped by disposing theconductor plates on the vertical and lateral sides of the fuse, thepresent invention is by no means limited thereto. More specifically, inan exemplary case where any other element resides on either of theleft-hand and right-hand sides of the meltdown portion of the fuse, itis also allowable to adopt a structure in which only the left-hand andright-hand sides are covered with the side plates 426, 427, whileleaving the upper and lower sides uncovered. In the case that any otherelement disposed on only either side of the left-hand and right-handsides, as far as prevention of the scattered conductor during the fusemeltdown is considered, it is all enough to provide the plate onlybetween the element in concern and the fuse. Even in such a case, it is,however, still preferable to dispose the plates both on the left-handand right-hand sides, and further on the upper and lower sides, in viewof confining the heat generated during the fuse meltdown in the vicinityof the fuse meltdown portion 407 and via-plug meltdown portions 423,453.

Also the fuse 400 may be composed of materials similar to those listedin the aforementioned first embodiment.

As has been described in the above, the first and second embodiment ofthe present invention, in which the meltdown portion of the fuse issurrounded by the plates, is successful in confining the heat generatedduring the meltdown in the vicinity of the meltdown portion, and inreducing the voltage or current for the fuse meltdown to a considerabledegree as compared with that required for the conventional semiconductordevice.

1. A semiconductor device, comprising: a substrate; a fuse formed over the substrate; a first conductive plate formed between the substrate and the fuse; and a second conductive plate formed over the fuse, wherein the second conductive plate overlaps the fuse in a plan view, the fuse comprises a pad and a first via which is connected to the pad, and the fuse is electrically isolated from the first conductive plate.
 2. The device as claimed in claim 1, wherein the fuse is copper.
 3. The device as claimed in claim 1, further comprising a first terminal which is connected to the first via; and wherein a width of the pad is narrower than a width of the first terminal.
 4. The device as claimed in claim 3, wherein the fuse is copper.
 5. The device as claimed in claim 3, further comprising: a second via which is connected to the pad; and a second terminal which is connected to the second via, wherein the width of the pad is narrower than a width of the second terminal in a plan view.
 6. The device as claimed in claim 5, wherein the first via and the second via are formed in the same dielectric layer.
 7. The device as claimed in claim 1, wherein the fuse is electrically isolated from the second conductive plate.
 8. The device as claimed in claim 7, wherein the interlayer dielectric layer is multilayer, and the second conductive plate is formed over the interlayer dielectric layer, and the fuse and the second conductive plate are sandwiching only a part of the interlayer dielectric film.
 9. The device as claimed in claim 8, wherein the fuse is copper.
 10. The device as claimed in claim 7, wherein the fuse is copper.
 11. The device as claimed in claim 1, further comprising a first and a second conductive walls that are sandwiching the fuse.
 12. The device as claimed in claim 11, wherein the fuse is copper.
 13. The device as claimed in claim 11, wherein the fuse is electrically isolated from the first and the second conductive walls.
 14. The device as claimed in claim 13, further comprising an interlayer dielectric layer formed over the substrate, and wherein the fuse and the first and the second conductive walls are embedded into the interlayer dielectric layer, the fuse and the first conductive wall are sandwiching only a part of the interlayer dielectric layer, and the fuse and the second conductive wall are sandwiching only a part of the interlayer dielectric layer.
 15. The device as claimed in claim 13, wherein the fuse is copper.
 16. The device as claimed in claim 14, wherein the fuse is copper. 